In a two-channel stereophonic home loudspeaker system, output from the two loudspeakers is dispersed into the large volume of the room, so the loudspeakers radiate independently. The same is generally true for multichannel systems with more than two channels. Typical stereophonic audio signals are predominately monophonic at low frequencies. As such, the acoustic outputs from the left and right channel bass outputs will add at the listener's ear.
However, when such loudspeaker systems are used in more confined spaces, the assumption that the loudspeakers radiate independently may not apply. This in turn may result in undesirable acoustic artefacts in the listening space, which can mar the listener's experience of the sound.
For example, an automotive audio system may consist of loudspeakers mounted in the left and right vehicle doors, as shown in FIG. 1. In such an arrangement, the vehicle cabin size will typically be much smaller than a home listening room, and the confined space can lead to unwanted acoustic effects, such that certain frequencies may not be perceived as strongly as others.
A conventional solution to such problems is often to boost the power to the loudspeaker, for example driving a bass transducer unit, such as a woofer. Although this can ameliorate the problem, it is not an efficient solution, as the sound system consumes more power and may require more bulky amplifiers. Moreover, it may lead to increased volume at frequencies at which it is not desired. Another solution for boosting bass sound can be to include a separate sub-woofer to generate the acoustic signal at low frequencies. In an automobile audio system, a subwoofer may be located in the floor of the vehicle cabin. Again, although the use of a sub-woofer can lead to better bass sound, the system does tend to consume more power and requires the additional transducer unit and drive electronics. In some types of vehicles, such as sports cars, the limited space may preclude the use of a sub-woofer.
EP 2357846 A1 describes a bass management system for automatically equalizing the group delay in the low audio frequency range generated by an audio system. The management system addresses the issue of aligning phase and/or group delay in the audio system and does so automatically, whereas it is more common to optimize such systems by hand, particularly in confined spaces such as a vehicle cabin.
Notwithstanding the various techniques described above, there is a need for a more effective and efficient technique for dealing with unwanted acoustic artefacts, which can arise when implementing multichannel audio systems in confined spaces. This is particularly true for systems producing high quality sound and located in a small cabin of an automobile.